The present invention relates to seals which are positioned against a moving surface, and more particularly to seals which prevent fluid, e.g. lubricant, leakage or passage between two surfaces. The seal includes a conductor, such as an optical or electrical conductor, for indicating that the body of the seal has undergone excessive wear or deterioration. The conductor is embedded within or attached to the body of the seal at a specified depth or location, namely the depth or extent of acceptable wear. The conductor may be an optical conductor, such as an optical fiber, or an electrical conductor, such as a wire or other means of conducting electricity. The continuity of the conductor can be checked to determine if the seal body has worn to the specified depth or been deteriorated beyond a specified extent.
Machinery often includes members which move with respect to each other. Bearings have long been used to facilitate such movement. Bearings are used to aid in transmitting forces from one member to another and to reduce friction. Rolling elements are often used in bearings to reduce friction, such as in ball bearings. Bearings often contain lubricant to reduce the friction created within the bearing.
Leakage of fluid from between mechanical parts has long been a problem. Contamination of the bearings or seals with foreign material such as dirt has also long been a problem. Both loss of fluid and contamination lead to increased friction and wear within the structure, damaging the structure and perhaps damaging the machinery.
Seals composed of a soft polymeric material are used with bearings to prevent lubricant leakage and contamination. The polymeric material contacts a moving surface in the bearing and provides a seal. Friction between the polymeric material and the moving surface gradually wears the surface of the polymeric material away. If the polymeric material becomes too worn, it will no longer form a tight seal against the moving surface, and fluid leakage from the bearing and contamination of the bearing again become problems.
In other instances metal or polymeric seals are placed between the moving parts. This arrangement is particularly useful when the movement is a reciprocal movement. Non-limiting illustrations of a reciprocating seal include a piston and cylinder structure, hatches, air locks, doors, covers, lids and caps. With regard to such seals as found in hatches, air locks, doors, covers, lids and caps, the interfitting members may be said to reciprocate with respect to each other, in the sense of opening and closing with regard to each other. However, when a seal is in fluid tight sealing relationship between such interfitting members, the seal may more properly be termed a static or stationary seal, since the interfitting members and the interposed seal are all stationary with regard to each other while the integrity of the sealing relationship is maintained. In certain types of members which are reciprocating with respect to each other, the seal may be made so that it always makes contact with the piston connecting rod and the connecting rod is electrically insulated from the piston barrel. Sealing integrity or effectiveness may also be compromised by cracking, breaking, loss of flexibility or deterioration due to such conditions as repeated flexing, bending and/or compression, or length of contact with various fluids or container contents.
Various methods have been developed to prevent or detect leakage past a seal. As shown in U.S. Pat. No. 4,761,023, one method involves monitoring the pressure of the fluid on the high pressure side of the seal, with a loss of pressure indicating leakage past the seal. Alternatively, as shown in U.S. Pat. No. 4,290,611, the fluid pressure on the low pressure side of the seal may be monitored, with an increase in pressure indicating fluid leakage. A third method, such as that shown in U.S. Pat. No. 4,178,133, uses colored fluid and visual monitoring of leakage past a seal. Still other methods involve manual maintenance procedures, wherein seals are inspected or replaced on a regular basis.
These various methods to prevent or detect leakage past a seal have not proven satisfactory due to a number of problems. A problem with monitoring fluid pressure is that it is only effective to detect leakage of the fluid. Often this is too late to prevent damage. It is desired that the seal be replaced before leakage has begun. Similarly, visual monitoring of fluid leakage can only indicate that leakage has begun, not that leakage is about to begin. A problem with manual inspection of a seal is that it requires an inspector who is not only trained but also diligent. Often seals are not inspected merely due to neglect or lack of diligence. Another problem with manual inspection is that it may require the machinery to be stopped during the inspection, which can be inconvenient. Scheduled seal replacement also has problems. Seals may wear more or less quickly depending on operating conditions, and scheduled seal replacement may occur too early (before the seal needs to be replaced) or too late (after the seal starts leaking).
An excellent solution to these problems has been provided by the inventions disclosed in my U.S. Pat. No. 5,540,448, issued Jul. 30, 1996, entitled SEAL WITH ELECTRICAL CONDUCTOR WEAR INDICATOR and in my U.S. Pat. No. 5,246,235, issued Sep. 21, 1993, entitled SEAL WITH EMBEDDED WIRE. The present invention is an improvement on my earlier disclosed seals and is particularly adapted to work with reciprocating surfaces which require a seal there between. Illustrative of such reciprocating surfaces are the piston and cylinder, hatches, air locks, doors, covers, lids, caps, etc.
The present invention provides a seal for recognizing excessive seal wear before fluid leakage occurs. The seal is placed between surfaces which may be moving or static with respect to each other and forms a seal with the moving surface or between the static surfaces to prevent fluid leakage. The seal includes a seal body and an optical or electrical conductor. The seal body is composed of a substance which allows it to make a seal with the adjacent surface. various conditions between the surface and the seal body cause gradual deterioration and/or wear of the seal body. For example, friction between a moving surface and the seal body may cause gradual wear of the seal body. Extended contact with a fluid or container contents may cause gradual deterioration or disintegration of the seal body. Aging of the seal material or repeated compression of the seal, as in continued forming and releasing of the seal, may cause gradual loss of resiliency, leading to cracking, breaking or splitting of the seal body.
The optical or electrical conductor may be embedded in the seal body, attached to the seal body or otherwise positioned so that deterioration of the seal body will gradually change the location of the conductor with respect to the adjacent surface or with respect to the surface of the seal body. Deterioration of the seal body to a specified depth can be detected by optical or electrical continuity of the conductor. An electrical conductor may contact the adjacent surface when deterioration of the seal body reaches a specified depth, with electrical continuity between the conductor and the adjacent surface indicating that the seal requires replacement. With an optical conductor attached to the seal, optical fibers will gradually be worn away as the seal wears. An optical sensor may be able to measure such parameters as wear, temperature or strain on the seal. Alternatively, the conductor may be positioned such that it is worn entirely through when the wear of the seal body reaches a specified depth, with loss of optical or electrical continuity through the conductor indicating that the seal requires replacement.
The present invention provides a simple, cost effective device and method to detect deterioration of a seal disposed between moving or reciprocating surfaces, avoiding the problems of previous devices. Because the device detects deterioration of the seal body rather than fluid leakage, the seal may be replaced prior to leakage. The problems associated with waiting until after leakage has begun before replacing the seal may be avoided. The seal may be replaced in a timely manner before leakage begins. Because the present invention is based on optical or electrical continuity, an optical or electrical signal circuit may easily be incorporated with the invention. The signal circuit may indicate to an operator when a seal needs to be replaced, and there is no problem with diligence on the part of an inspector. Because wear of the seal body may be determined without manual inspection, problems with training inspectors and with missed or failed inspections are avoided. There is also no need to stop the equipment or machinery just to check if the seal needs to be replaced. Because the present invention monitors the actual amount of deterioration on the seal body, there is no problem with early or late replacement of the seal based on a scheduled replacement program. Replacement of the seal of the present invention may be based on the actual life of the seal body in operation, not on an average seal body life. Seals may be replaced less often and cost is reduced.
The present invention provides a seal for preventing passage of a fluid between two members. The seal is in engaging contact with both members to prevent passage of fluid between the two members and the seal. The seal is adapted to retain a fluid tight seal with the members so long as the seal has not deteriorated beyond a specified degree. A conductor is placed around one of the members. The conductor serves to conduct a signal. The conductor is positioned with respect to the seal such that deterioration of the seal beyond a specified degree corresponds with signal discontinuity of the conductor. The signal discontinuity through the conductor indicates a requirement for replacement of the seal. The seal may be an electrical signal or an optical signal.